1. Field of the Invention
The present invention is directed to a method for localizing at least one focal lesion in a biological tissue section, the lesion exhibiting an electrical property different from the tissue section and whereby the electrical property in the tissue section being essentially constant.
2. Description of the Prior Art
A method for this purpose is disclosed in PCT Application WO 99/48422. In this method a sequence of electrical excitation signals with different frequency is applied to the tissue section, electrical response signals are measured at multiple measurement locations at a surface of the tissue section that occur thereat due to the excitation signals, frequency-independent signal parts in the response signals are determined and further-processed to produce input values for a localization step, and the tissue section is modeled and a set of lead fields is determined. For imaging by means of electrical impedance measurement, electrical currents are impressed and/or voltages applied to an examination subject (patient) at one or more locations. Voltages that arise due to the impressed currents are measured with M electrodes (M≧1) that are brought into electrical contact with the tissue section under examination at one or more locations. Currents that occur due to the applied voltages can be alternatively or additionally measured. The voltages and/or currents are defined for the subject (defined, for example, by a complex conductivity in the mathematical sense). Measured data thus are obtained at M different locations.
Spatial data (current values and/or voltage values) at different frequencies can be obtained by supplying at least one time-variable current and/or by applying at least one time-variable voltage. Frequency-dependent, measured spatial data are acquired in this way as a result of the frequency dependencies of the electrical conductivity that are typical for particular tissues. M×N data are obtained in the case of M measured data at N frequencies. As occurs, for example, given the TS2000 device of the TransScan Company, such data can be converted into time-independent susceptance values and capacitance values, i.e. into admittance values, and can be presented in conformity with the 2-dimensional electrode arrangement.
In a localization method of the type initially described an object of the invention is to increase the localization precision.